can a resistor solve this problem? 3

[mick43]

I want to operate a 24 volt device from a 48 volt power supply.

Manual says device (a carbon dioxide sensor) will operate at 18-30 vdc (or20-28 Vrms AC) and power consumption is listed at "less than 2 watts @ 24 VAC."

Most of the power consumption seems to be from a "heater" that pulses on and off (about two times per second) to keep an exact temperature in the sensor module.

When running with a 24 vdc power supply, my digital meter (set on 10 amp) flashes between .04-.05 of current.

However, at a preset level of carbon dioxide, a control relay closes. When the relay is closed, the reading flashes between .06-.07.

Is it possible to drop the voltage into the 18-30 volt range with a resistor when the load varies like this?

Thanks for any help with this question.

Mick43

 

[OperaHouse]

I don't think you understand the concept. The microprocessor changes the time interval based on the CO2 level. You can even turn on any number of fans based on the level and adjust the time period. The microprocessor can easily learn the enviroment it is placed in. People fail to understand how smart these systems can be. I envision a nice safe system: A UL wall transformer to provide safe 24V to the box and sensor with low voltage lines going to solid state relays that turn a number of fans on and off. Nice, simple, easy to sell safe, and limited liability. What you have is a maintenance nightmare.

 

[nbucska]

Hi Mick
Yes I am very interested in mushrooms and have a few questions and suggestions.

If you give me the detailes specs I can design the
power supply for you -- free, of course.

Nick



<nbucska@pcperipherals DOT com> subj: eng-tips
read FAQ240-1032

 

[buzzp]

One thing to clarify on your DC contacts, the making of the circuit is not usually as harsh as breaking the circuit. Just thought I would clarify this based on your comment concerning the motor is not starting until 5 seconds after the relay closes. Often, they will have a "make" rating and a "break" rating.

 

[mick43]

Thanks to buzzup and OperaHouse for comments about switching 48 vdc. Based on your comments, I think I'll abandon both the idea of switching 48vdc, and, abandon the idea of dropping 48vdc to 24 vdc to power the sensor.

I was hoping to find a small, solid state device that could simply and inexpensively drop the dc voltage. But after testing a working model and coming to realize the amount of heat generated, then remembering
dhwilliams' comments about protection for the circuit, and buzzup's and OpreaHouse's comments about the problems associated with switching 48vdc, I will give up this idea.

I'll just use a bigger "box" and install a 24vac transformer (instead of solid-state stuff) to power the sensor, and, to supply power for a 24vac relay that will switch the 120vac primary input to the 48vdc power supply.

Mick 43